Wear layers previously employed on vinyl floor and wall tile have certain inherent deficiencies that render them unsuitable for general application. For example, thermoplastic wear layers lower the resistance of the tile to scorching from hot objects such as a burning cigarette. In addition, the solvent resistance of such coated tiles is generally relatively poor. Tiles having such coatings of adequate thickness thereon are also found to have serious dimensional stability problems in the form of undesirable curling of the edges of the tile in storage or service.
Polymerizable coatings that require conventional organic solvents are unsuited for vinyl floor tiles because the penetration of coating solvent into the vinyl base material tends to lower the resistance of the tile to indentation. Even after heat treatment, the tile contains a residual amount of solvent that adversely affects the flow and indentation properties of the finished tile in service.
Heat cured coatings have been found to induce curling problems in vinyl tile caused, at least in part, by the shrinkage of the surface wear layer during polymerization. Such problems are complicated by any lack of uniformity in coating thickness.
Electron beam, gamma radiation and x-ray treatment have also been proposed to initiate curing and to promote cross-linking of surface coatings on vinyl tile. Such irradiation techniques are not acceptable. Such methods tend to discolor the base surface and promote extremely rapid polymerization. The resulting coating shrinkage appears to place the tile surface under tension such as to cause undesired curling or cupping of the tile.
Vinyl tile as usually prepared contains a polyvinyl chloride resin or a copolymer of polyvinyl chloride and polyvinyl acetate. Stabilizers are usually incorporated in an amount ranging from about 0.3% to about 1.5% by weight of said base tile. While such tile is relatively free of the curling difficulties encountered in the various attempts to apply a clear wear layer to the tile, such tile must be cleaned and waxed at regular intervals to preserve its appearance in use.